There's two things wrong in this statement.
1) In Hebrew the word translated as "circle" actually means circle, as in a round, flat plane. There is a word in Hebrew for "ball", which isn't the word Isaiah uses. The cosmological view of the time was consistent with what other ancient near eastern cultures thought, and that is the language the writers of Holy Scripture use.
2) Columbus didn't discover that the earth was round, everyone with a basic education at the time already knew that; we've known this in the West since at least the time of Eratosthenes who demonstrated the spherical shape of the earth 2300 years ago. The idea that medieval people believed the earth is flat is a popular modern myth--and the idea that Columbus set out to prove the earth was round is pure fiction, invented out of imagination in the 1800s. The reality is that Columbus believed the earth was much smaller than it is (Eratosthenes' experiments also mathematically gave us the size of the planet as well, and he was remarkably close to the actual figure, being off by only a few percent). Columbus' unfounded belief that the earth was about 1/3 smaller than what was accepted led him to believe that it was possible to reach India by sailing west--no one doubted that you could in theory reach Asia by sailing west at the time, but the distance alone made that an utterly suicidal mission to attempt (imagine sailing in a relatively primitive wooden vessel across both the Atlantic and Pacific Oceans with no Americas in between). After being rejected by other European rulers, and even by the Spanish Crown several times, they finally agreed and gave him a few boats to go on his suicidal trip. Columbus was wrong, he merely got lucky to bump into a Caribbean island. Well, lucky for him, very unlucky for the indigenous peoples. Christopher Columbus is one of history's most evil tyrannical monsters.
-CryptoLutheran